1. Field of the Invention
The present invention relates to a machine tool having at least one machine part which undergoes temperature-dependent changes in length.
2. Related Prior Art
Machine tools of this kind are commonly known.
The problem of so-called thermal deflections occurs in almost all machine tools. When these machine tools are operated, certain machine parts heat up because of the heat generated in the working space due to the hot chips and the equipment being run. This heating in turn results in changes in length, which cause elongations to occur inside the machine tool.
A change in length in a guide rail, for example, can cause the position of an end switch or reference point to shift, so that all the concatenated dimensions dependent thereon become inaccurate. It is furthermore possible for the spacing between the workpiece table and the spindle axis to change, so that, in a manner of speaking, the preset machine parameters change.
The machining accuracy of the machine tool is thereby influenced, since in some circumstances the control system is proceeding from incorrect parameters. These thermal deflections vary depending on coolant use, number of operator door openings required, ambient temperature in the building, coolant temperature, etc., so that they cannot be completely compensated for by presettable parameter sets.
It is already known to sense this so-called temperature response instrumentally, and compensate for it on the basis of empirical values. For this purpose the applicant uses its method called "Thermocontrol," which is based on temperature and reference measurements, to take into account previously measured, known temperature responses in the control system. In the simplest case, the machine parameters to which the control system refers are modified as a function of temperatures measured in the working space of the machine tool.
It has now been found that although slow, low-amplitude temperature responses can be compensated for with this method, large temperature changes cannot be balanced out in this fashion.